1. Field of the Invention
The present invention relates to a broadcasting and communication system, and more particularly, to a method and an apparatus of modulating a digital signal for transmission of the digital signal in a broadcasting and communication system.
2. Related Art
A modulation technology that is currently being used in a broadcasting and communication system may be mainly divided into a modulation technology using a single transmission channel and a modulation technology using two transmission channels. The modulation technology using a single transmission channel has a real (Re) axis in a signal constellation and includes a modulation technology such as vestigial side band (VSB), or the like. The modulation technology using two transmission channels has a real (Re) axis and an imaginary (Im) axis in a signal constellation and includes a modulation technology such as quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK), or the like. Recently, the modulation technology using two transmission channels capable of variously changing transmission capacity, such as QAM and QPSK has been mainly used.
Meanwhile, a layer modulation technology may be applied in modulating a digital signal. The digital video broadcasting-terrestrial (DVB-T) transmission standard of Europe includes a layer modulation technology. However, the layer modulation technology may also be applied to other fields that are not included in a transmission standard. The layer modulation technology may be applied in order to transmit additional data in addition to originally transmitted data. For example, the layer modulation technology may be applied as a combination of QPSK+QPSK, 16 QAM+QPSK, or the like. That is, main data and additional data may be transmitted in a scheme of modulating the main data using a QPSK or 16 QAM modulation technology, modulating the additional data using a QPSK modulation technology, and combining them with each other. When the layer modulation technology is applied, backward compatibility between a base layer and an additional layer is secured. The backward compatibility is secured, such that users having existing receivers may be protected. Even though the additional layer is added to a transmitting end, in addition to the base layer, separate reception signal processing for demodulating the base layer signal is not required at a receiving end. The reason is that when the base layer signal is demodulated at the receiving end, the additional layer signal acts as noise, such that it does not have an effect on demodulation of the base layer signal.
Therefore, a modulation and demodulation method in which a layer modulation technology is applied in order to transmit additional data in a communication and broadcasting system may be suggested.